A radioaltimetric height being provided by an on-board radioaltimeter, to be further described below, can be used for numerous systems on-board the aircraft, and including for critical systems such as the automatic piloting system or flight controls. In the case of an erroneous radioaltimetric height (given as valid, but having its value being false), the pilot could be led to manage a work overload, upon critical flight phases, linked to a landing.
A radioaltimeter is an avionic system having, as a function, to calculate the height of the aircraft at the vertical above the ground. This system is based on a pulse or ramp modulation at the vertical of the current position of the aircraft. More precisely a high frequency radioelectric source emits, from the aircraft, a modulated signal, and the measurement of the time separating such an emission from the reception of the ground echo, allows the distance (height) to be calculated with respect to the ground.
In particular, during an approach and landing phase of an aircraft, the radioaltimetric height aids to the follow-up of the vertical trajectory and to the upholding of the descent slope. It is used, generally and mainly, in managing mode engagements, laws of flight controls, and of the automatic piloting system, and becomes a primary parameter in the law managing the final flare-out before landing.
Generally speaking, the architecture to be used on aircrafts for providing a radioaltimetric height is structured around several radioaltimeters so as to ensure availability and integrity of the radioaltimetric height, according to the requirements of the functions of the aircraft, to which implementation it takes part.
In particular, a two radioaltimeter architecture (having each of them that transmits its measurements, for example, to two guiding systems, to two display systems, . . .) allows to ensure an integrity and an availability of the height information, sufficient with respect to the needs.
However, some malfunctions resulting in an erroneous radioaltimetric height, can generate, even if they are detected, a work overload for the pilots, such as for example the need to manage a throttling up again, near the ground, before landing. Such malfunctions could correspond to an internal malfunction of a radioaltimeter or to particular external conditions that are to affect the radioaltimetric signal.
Nevertheless, there already are means for monitoring radioaltimetric heights that compare therebetween the data supplied by two radioaltimeters for the most critical flight phases, and that warn the crew should a difference occur (resulting in the aircraft being again under control) without however specifying the defective radioaltimeter. Such usual monitoring means do thus not allow to ensure an operational continuity of the approach through switching to the not defective radioaltimeter.
Moreover, such architecture does not supply any height information other than those generated by the radioaltimeters. Thus, should an error occur as a result of an origin common to the different radioaltimeters, no radioaltimetric height is available to be exploited on-board the aircraft.
The present invention relates to a method for monitoring radioaltimetric heights of an aircraft, allowing the above mentioned drawbacks to be overcome.